Cu/Nb纳米多层膜延性及其断裂行为

通过单轴拉伸试验研究恒定调制周期的聚酰亚胺基体Cu/Nb纳米金属多层膜的延性对调制比的依赖性,并采用聚焦离子束／扫描电子显微镜(FIB/SEM)截面定量表征技术深入分析多层膜的异质约束效应对断裂行为的影响.结果表明随着调制比的增加,多层膜的延性单调减小,出现由剪切型向张开型断裂模式的转变.当调制比小于某一临界值时,调制周期越小,多层膜延性越高;反之,则多层膜延性越差.这是由于软相Cu层对脆相Nb层中萌生的微裂纹扩展的约束作用.     

不同调制波长Cu/Ag多层膜硬度分析

用直流电沉积双槽法在纯铜基体上制备了不同调制波长的Cu/Ag多层膜,研究了多层膜硬度与调制波长之间的关系.实验结果表明,当调制波长位于600～300nm时,Cu/Ag多层膜的硬度与调制波长之间较好地符合基于位错塞积模型的Hall-Petch关系;当调制波长小于300 nm时,硬度与调制波长的关系偏离了HaU-Petch关系.由实验结果分析得出了Cu/Ag多层膜的位错稳定存在极限晶粒尺寸约为25 nm,与基于程开甲等人的位错稳定性理论得出的Ag晶体极限晶粒尺寸27 nm接近,验证了程开甲等人的位错稳定性理论.     

Ag/Cu和Cu/Ni纳米金属多层膜强度软化的理论分析

用电沉积法分别制备了具有不同调制波长的Ag/Cu和Cu/Ni金属多层膜,研究了多层膜的硬度与调制波长之间的关系.结果表明,当调制波长λ>300 nm时,两种多层膜的硬度与调制波长符合位错塞积机制的Hall-Fetch关系,当λ<300 nm时,都偏离了Hall-Fetch关系;Ag/Cu和Cu/Ni多层膜分别在λ=50nm和100nm处取得硬度峰值.基于Cheng等人的电子理论分别求出了Ag,Cu和Ni金属晶体的位错稳定的临界晶粒尺寸,进而定量地解释了Ag/Cu和Cu/Ni金属多层膜硬度峰值位置.     

双槽电沉积法制备Cu/Ag纳米多层膜

双槽电沉积法制备了不同调制波长的Cu/Ag金属多层膜(Cu膜和Ag膜等厚),用扫描电子显微镜观察了多层膜的层状结构,并研究了不同调制波长下多层膜的显微硬度变化.结果表明:双槽电沉积法制备的Cu/Ag多层膜层状结构明显.当调制波长大于100 nm时,显微硬度随调制波长减小而增加;当小于100 nm时,硬度随调制波长减小而...     

Cu/X(X=Cr,Nb)纳米多层膜力/电学性能的尺度依赖性

利用纳米压痕实验以及四探针法,系统研究了相同层厚Cu/X(X=Cr,Nb)纳米金属多层膜的力学性能(强/硬度)和电学性能(电阻率)的尺度依赖性.微观分析表明:Cu/X多层膜调制结构清晰,Cu层沿{111}面择优生长,X层沿{110}面择优生长.纳米压入结果表明,Cu/X多层膜的强度依赖于调制周期,并随调制周期的减小而增加.多层膜变形机制在临界调制周期(λ~c≈25 nm)由Cu层内单根位错滑移转变为位错切割界面.多层膜的电阻率不仅与表面/界面以及晶界散射相关,而且在小尺度下受界面条件显著影响.通过修正的FS-MS模型可以量化界面效应对多层膜电阻率的影响.Cu/X纳米多层膜可以通过调控微观结构实现强度-电导率的合理匹配.     

Cu/Ni和Cu/Nb纳米多层膜的应变率敏感性

为研究调制周期和界面结构对纳米多层膜应变率敏感性的影响,采用电子束蒸发镀膜技术在Si基片上制备了不同周期(Λ=4 nm,12 nm,20 nm)的Cu/Ni纳米多层膜,采用磁控溅射技术在Si基片上制备了不同周期(Λ=5 nm,10 nm,20 nm)的Cu/Nb纳米多层膜。在真空条件下,对Cu/Ni纳米多层膜进行了温度分别为200和400℃、时间4 h的退火处理,对Cu/Nb纳米多层膜进行了温度分别为200、400和600℃,时间为4 h的退火处理。采用XRD和TEM表征了Cu/Ni和Cu/Nb纳米多层膜的结构,采用纳米压痕仪获取了不同加载应变率(0.005、0.01、0.05和0.2 s~(-1))下纳米多层膜的硬度。结果表明,应变率敏感性受到界面结构和晶粒尺寸的影响,非共格界面密度提高以及晶粒尺寸变大均可导致应变率敏感性下降。当周期变大时,Cu/Ni纳米多层膜的非共格界面密度提高,晶粒尺寸变大,应变率敏感性指数m减小;当周期变大时,Cu/Nb纳米多层膜的非共格界面密度下降,晶粒尺寸变大,m基本不变。随退火温度上升,Cu/Ni和Cu/Nb纳米多层膜应变率敏感性大体上呈现下降趋势,这是由退火过程中非共格界面密度上升和晶粒长大共同引起的。     

调制波长对Cu／Ni金属多层膜力学性能的影响

用电沉积法在低碳钢基体上制备了具有不同调制波长(一个调制波长等于单层Cu膜与单层Ni膜厚度之和)的Cu/Ni金属多层膜，研究了多层膜硬度与其中单层膜厚度之间的关系。结果表明，当膜厚在亚微米范围内时，Cu/Ni多层膜的屈服强度(为硬度值的1/3)与单层膜厚之间符合基于位错塞积模型的Hall-Pctch(H-P)关系式；而当单层膜厚小于100nm时，屈服强度与膜厚的关系偏离了H-P线性关系。基于程开甲等人位错稳定性理论首次对金属多层膜变形行为偏离Hall-Petch关系的现象作了定量解释。     

Cu/Ni多层膜对Ti811合金微动磨损和微动疲劳抗力的影响

在Ti811钛合金表面利用离子辅助磁控溅射沉积技术制备20～1200nm不同调制周期的Cu/Ni金属多层膜,分析多层膜的结构,测试膜基结合强度、膜层显微硬度和韧性,对比研究不同调制周期的Cu/Ni多层膜对钛合金基材常温下微动磨损性能和微动疲劳(FF)抗力的影响。结果表明:利用离子辅助磁控溅射技术可以获得致密度高、晶粒细化、膜基结合强度高的Cu/Ni多层膜,该类多层膜具有良好的减摩润滑作用,因而改善了Ti811钛合金常温下抗微动磨损和微动疲劳性能;Cu/Ni多层膜对钛合金FF抗力的改善程度随膜层调制周期呈现非单调变化趋势,调制周期为200nm的Cu/Ni多层膜对钛合金FF抗力的提高程度最大,原因归于该膜层具有良好的强韧和润滑综合性能。     

Cu/Ni多层膜在多冲与压压载荷下的失效行为

采用磁控溅射技术在TC4钛合金表面制备Cu/Ni多层膜,利用多冲和动态循环压压试验装置对膜层的力学性能进行了评价,探讨了冲击条件、多层膜调制周期及结构等对多层膜失效行为的影响,比较了多层膜和单层Cu、Ni膜在多冲条件下的失效行为,以及多冲与循环压压载荷对多层膜失效行为的影响.结果表明:多冲法能够较好地表征Cu/Ni多层膜的结合强度、韧性、内聚强度.压压载荷作用下多层膜的失效主要表现为单一的开裂现象,因而压压法更适合评价膜层的韧性.采用合适的过渡层、离子辅助和基材加热方法可以获得高的多层膜强度和韧性;调制周期小于600 nm的Cu/Ni多层膜的内聚强度、韧性及多冲承载能力高于Cu、Ni单层膜;调制周期小于200 nm的多层膜呈现出明显的超硬度现象,且具有良好的强韧性能.     

Cu/Ni多层膜中交变应力场对可动位错的制约

Cu／Ni多层膜的强化作用来自于多层膜结构中交变应力场对位错运动的约束．该交变应力场主要包括两部分：在共格界面处由于剪切模量差而导致的镜像力，以及多层膜内由于晶格常数差而形成失配位错网的应力．如果位错在膜层内运动的临界应力值小于交变应力场的约束，位错会被限制在单层膜内运动，多层膜被强化；反之，则位错很容易通过界面到达临近的膜层，多层膜开始出现弱化．交变应力场的变化幅值与多层膜的调制波长相关．理论计算结果表明，Cu／Ni多层膜的临界调制波长为1．9nm，但失配位错网的交变应力场在多层膜的调制波长λ=9nm时振幅达到极值．     

Length-scale-dependent deformation and fracture behavior of Cu/X (X = Nb, Zr) multilayers: The constraining effects of the ductile phase on the brittle phase

The plastic deformation and fracture behavior of two different types of Cu/X (X = Nb, Zr) nanostructured multilayered films (NMFs) were systematically investigated over wide ranges of modulation period (λ) and modulation ratio (η, the ratio of X layer thickness to Cu layer thickness). It was found that both the ductility and fracture mode of the NMFs were predominantly related to the constraining effect of ductile Cu layers on microcrack-initiating X layers, which showed a significant length-scale dependence on λ and η. Experimental observations and theoretical analyses also revealed a transition in strengthening mechanism, from single dislocation slip in confined layers to a load-bearing effect, when the Cu layer thickness was reduced to below ∼15 nm by either decreasing λ or increasing η. This is due to the intense suppression of dislocation activities in the thin Cu layers, which causes a remarkable reduction in the deformability of the Cu layers. Concomitantly, the constraining effect of Cu layers on microcrack propagation is weakened, which can be used to explain the experimentally observed λ and η-dependent fracture mode transition from shear mode to an opening mode. Furthermore, the fracture toughness of the NMFs is also found to be sensitive to both λ and η. A fracture mechanism-based micromechanical model is developed to quantitatively assess the length-scale-dependent fracture toughness, and these calculations are in good agreement with experimental findings.     

调制周期对Ti/TiB_2多层膜的结构和力学性能的影响

采用磁控溅射法制备了Ti/TiB_2周期性(T=2,3,4,6,12)多层膜,利用X射线衍射仪、场发射扫描电子显微镜分析了薄膜的相结构和表面(断面)形貌,采用纳米压痕仪、多功能摩擦摩损试验机和显微硬度计研究了多层膜的纳米硬度、弹性模量、膜基结合力以及断裂韧性。结果表明:Ti/TiB_2多层膜具有清晰的纳米层状结构,薄膜表面致密平整,与基体保持着良好的物理结合。多层膜的硬度和弹性模量随着调制周期的增加而增大,在周期T=12时,多层膜的硬度和弹性模量达到最大值,分别为35.8和349 GPa;多层膜的断裂韧性随着周期的增加呈现出先增大而后减小的趋势,当周期T=6时多层膜的断裂韧性最好,其断裂韧度为2.17 MPa·m~(1/2)。分析认为多层膜中的Ti子层可使裂纹尖端产生钝化作用,从而引起裂纹扩展路径发生偏转,提高了多层膜的断裂韧性。     

Interfacial Structures Governed Plastic Deformation Behaviors in Metallic Multilayers

In this work, we have investigated the mechanical properties of Cu/Ta, Ag/Cu and Ag/Nb multilayers with different heterogeneous interfaces. The results suggest that when individual layer thickness(h) is larger than 5–10 nm, the hardness/strength of three different multilayer systems has the similar length scale effect with decreasing layer thickness,while when h B 5 nm, the three multilayer systems show remarkably different plastic deformation behaviors. The strength curves exhibit the variation trends of unchanging, softening and increasing corresponding to Cu/Ta, Ag/Cu and Ag/Nb multilayers, respectively. The microstructure analysis shows that three kinds of multilayers have totally different interfacial structures, which lead to the different strengthening or softening mechanisms.     

Solid state amorphization in cold drawn Cu/Nb wires

The microstructure of cold drawn Cu/Nb nanocomposite wires was investigated using a three dimensional atom probe (3D-AP) and transmission electron microscopy (TEM). Although there is no solubility between Nb and Cu in the equilibrium state, atom probe analysis results revealed that intermixing occurs between Nb and Cu filaments as a result of cold drawing with a large strain. High resolution transmission electron microscopy (HRTEM) results revealed that an amorphous layer is formed along some Cu/Nb interfaces. This solid state amorphization is compared with similar reactions observed in Cu–Nb multilayers.     

Buckling behaviors and adhesion energy of nanostructured Cu/X (X = Nb,Zr) multilayer films on a compliant substrate

Two sets of Cu/Nb (face-centered cubic (fcc)/body-centered cubic) and Cu/Zr (fcc/hexagonal close-packed) nanostructured multilayer films (NMFs) have been prepared on a flexible polyimide substrate, with a wide range modulation period (λ) from 250 down to 5 nm. The mechanical properties of the two NMFs have been measured upon uniaxial tensile testing and the buckling behaviors have been systematically investigated as a function of λ. A significant difference in the bucking behaviors was found between the two NMFs, with the buckles in the Cu/Nb NMF being mostly cracked, while the buckles were nearly crack-free in the Cu/Zr NMF. The different buckling behaviors, dependent on the constituent phases, are rationalized in the light of the disparity in mechanical properties. The criteria to characterize buckle cracking have been discussed with respect to the mechanical properties (e.g. yield strength, ductility and fracture toughness) of the NMFs. A modified energy balance model has been employed to estimate the adhesion energy of the NMFs on the polyimide substrate. Within the λ regime below a critical size (λ_crit) of ～50 nm a λ-independent adhesion energy of about 1.1 and 1.2 J m^?2 has been determined for the Cu/Nb and Cu/Zr NMFs, respectively, which agrees well with previous reports on the metal film/polymer substrate systems. Within the λ regime greater than λ_crit, however, the measured adhesion energy exhibit a strong size effect, i.e. increasing with increasing λ. The λ dependence of the evaluated adhesion energy is discussed in terms of the size-dependent deformation mechanism in NMFs. A micromechanics model has been utilized to quantify the critical modulation period of ～50 nm, where the deformation mechanism changes from dislocation pile-up to confined layer slip.     

On plasticity and fracture of nanostructured Cu/X (X = Au,Cr) multilayers: The effects of length scale and interface/boundary

Plastic deformation and fracture behavior of two different types of Cu/X (X = Au, Cr) multilayers subjected to tensile stress were investigated via three-point bending experiments. It was found that the plastic deformation ability and fracture mode depended on layer thickness and interface/boundary. The Cu/Au multilayer showed significant features of plastic flow before fracture, and such plasticity was gradually suppressed by premature unstable shearing across the layer interface with decreasing layer thickness. In comparison, Cu/Cr multilayers were prone to a quasi-brittle normal fracture with decreasing layer thickness. Both experimental observations and theoretical analyses revealed differences in plasticity and fracture mode between the two types of metallic multilayers and the relevant physical mechanism transition due to length scale constraint and interface/boundary blocking of dislocation motion.     

调制周期对CrAlN/ZrN纳米多层膜韧性的影响

目的研究调制周期对纳米多层膜性能的影响。方法采用磁控溅射方法制备了CrAlN与ZrN的固定厚度比为2.6,不同调制周期(Λ为6,8,10,20 nm)的CrAlN/ZrN纳米多层膜。利用场发射扫描电镜(FESEM)表征薄膜的形貌、结构。用Dektak150型台阶仪测薄膜表面粗糙度。用Agilent Technologies G200纳米压痕仪检测涂层的硬度和弹性模量。用划痕仪测薄膜/基材的结合力,同时,引入抗裂纹扩展系数(CPR)表征纳米多层膜的韧性。结果 CrAlN/ZrN纳米多层膜断面皆为穿晶柱状结构,调制周期为20 nm时,多层膜层与层之间的界面清晰;多层膜表面呈致密的花椰菜状,厚度均约为2μm。调制周期为8 nm时,硬度为20.4 GPa,进一步增大调制周期,硬度下降。调制周期为8 nm的多层膜临界载荷L_(c2)为18 N,CPR值为73.2,L_(c2)与CPR值均高于其他调制周期的多层膜。在临界载荷L_(c2)处,裂纹扩展导致薄膜发生了严重的片状剥落,露出了亮白的热轧钢基底,薄膜失去了保护作用。结论实验表明,在多层膜厚度、调制比不变的条件下,改变调制周期能够改变多层膜的韧性。随着调制周期的增大,韧性呈先上升、后下降的趋势。调制周期为8 nm时,纳米多层膜的硬度最高,韧性最好,综合性能良好。